Reactivity of Highly Lewis‐Acidic Diborane(4) toward C≡N and N=N Bonds: Uncatalyzed Addition and N=N Bond‐Cleavage Reactions

Abstract

The diboration of the C≡N bond in organic nitriles, and the N=N bond in azobenzene and pyridazine, by the highly Lewis‐acidic tetra(o‐tolyl)diborane(4) are reported. In the reactions with nitriles, azobenzene, and pyridazine, the addition of diborane(4) to the C≡N and N=N bonds was observed. Conversely, the N=N bond in phthalazine was cleaved by an addition/rearomatization sequence.

A Neutral and Aromatic Boron‐Rich Inorganic Benzene

“…In the (3) ). [20] The phosphine-bonded boron atoms (B2 and B3) are attached to the central carbon atoms of diphenylacetylene, confirming that a [4+2] cycloaddition reaction took place between 3 and PhCCPh. We also observed a similar cycloaddition reaction between 3 and CO 2 .…”

Electron‐Rich, Lewis Acidic Diborane Meets N‐Heterocyclic Aromatics: Formation and Electron Transfer in Cyclophane Boranes

“…The recently reported reaction of the highly Lewisa cidic tetra(o-tolyl)diborane(4) with phthalazine in toluene yielded the first N,N'-diboryl-2,3-dihydrophthalazine (after 10 min reaction time) and then in 8h 1,2-bis(borylimidoyl)benzene, in which the NÀNb ond wasc ompletely cleaved. [30] In contrast, the reactionof1 with phthalazine resulted in the complexation of one phthalazine molecule to give monocationic diborane(4) derivative 3 in 90 %y ield as yellow crystals (Scheme 2). This re-action offers ac onvenient access to asymmetricd iboranes by substitution of the remaining triflato substituent.…”

Sterically Unprotected Nucleophilic Boron Cluster Reagents

“…However, in metalcatalyzed borylations of alkyl electrophiles, pseudohalides are rarely reported as substrates due to the reduced reactivity of C sp 3 -O bonds towards activation by several metal-based catalysts commonly employed under borylation conditions 20 . In our case, the substitution of both primary and secondary alkyl-OTs/OMs substrates by B 6 H 6 2-(16) proceeded smoothly in the absence of any metal salts or halide additives; subsequent cage deconstruction produced the corresponding pinacol boronate ester compounds (33)(34)(35)(36)(37)(38) (Fig. 3c).…”

“…This led us to the development of a simple protocol, whereby carbon-based electrophiles can be transformed into the corresponding tricoordinate boron ester species without the use of metal catalysis. This work highlights how boron-rich clusters can expand the toolkit of main group reagents [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] ultimately aiding in the development of organic synthesis through new modes of reactivity.…”